In diagnosing a patient suffering from an injury or a condition generally affecting a major limb, doctors, physical therapists, and other health care workers find it useful to analyze data related to motion characteristics of the affected limb's joint.
Devices have long been available which aid in the measurement of relative angular position or angular displacement of a patient's joint. The first of these devices were simple in structure comprising essentially two arms pivotally connected at a hinge with one of said arms having a gage extending therefrom and intersecting the other arm to provide a mechanical readout of angular position similar to that provided by a protractor. The early devices were simply applied across a fully contracted, then a fully extended pair of body part members. By noting the difference between the contracted-position and extended-position measurements users of such devices were able to roughly estimate angular displacement. The first patient-worn angular displacement measuring devices were rather crudely attached to subject body part members and measured angular position by the same mechanical, protractor-like means.
The past two decades have seen considerable activity in the improvement of devices capable of measuring the angular displacement between two body part members connected at a common joint. U.S. Pat. No. 4,436,099, Raftopoulus, describes an improved support means for patient-worn angular displacement measuring devices. The improved device overcomes deficiencies of prior devices whose support means, it is said, encumbered natural body part movement and therefore gave rise to distorted measurements of angular displacement. The Raftopoulus patent also describes means for digitally displaying angular position and displacement comprising an encoder in combination with a counter circuit and a display unit.
U.S. Pat. No. 4,442,606, Graham et al., describes a device for measuring the angle made by two bones connected at a common joint comprising two arms connected by a rotary potentiometer. The potentiometer output is fed through a decoding device and then to a digital readout device. Preferably, the potentiometer output is simply inputted into a digital voltmeter whose gain is adjusted such that its display indicates relative angular position, either in degrees or radians.
U.S. Pat. No. 4,667,685, Fine, describes a therapeutic device providing visual feedback to a patient exercising an injured joint. An analog signal generated by a transducer mounted to a brace mechanism activates a series of light-emitting diodes in succession as a patient moves his or her joint to increase the transducer's output voltage. By observing the LED array, a patient is provided a graphical representation of angular displacement, and an indication of the distance needed to be moved to reach a preset target displacement angle.
The usefulness of data respecting the range of motion of a patient's injured joint has long been recognized. Fortunately, as the cited prior art illustrates, devices are now available which greatly improve the ease and the accuracy with which joint position and displacement information is obtained and displayed. But while devices currently available reliably measure and display data pertaining to the range of motion of a patient's joint, none of the devices described in the cited prior art can measure and display data pertaining to the speed with which a patient's joint is moved.
Obtaining a measurement for angular velocity of joint-connected body part members with currently available devices requires complex data manipulation. One publication that recognizes the usefulness of data respecting angular velocity of a moving joint, U.S. Pat. No. 5,012,819, Marras et al., describes a device which can record the angular position versus time, relative to a predetermined start position for each of any three planes of motion of a human spine. Failing to teach a means for electronic measurement and display, the Marras patent discloses that the rate of angle change of any of the three planes of spine movement can be calculated by analyzing the data pertaining to position versus time for the subject plane, then differentiating said data to obtain a value for instantaneous angular velocity at any point in time.
In view of the fact that important diagnostic information can be gained by observing data pertaining to the speed with which a joint is moved which cannot otherwise be gained by merely observing the range of motion of body part members connected at said joint, it is a principal object of the present invention to provide, without complex data manipulation, a device which electronically measures and displays the average angular velocity of a moving joint.